Optical mouse and image capture chip thereof

ABSTRACT

An optical mouse and image capture chip thereof. The image capture chip comprises an image sensor, a calculating logic circuit, and a refreshing logic circuit. The image sensor has a plurality of sensor units, capturing an image according to an exposure parameter to provide a plurality of exposure values. The calculating logic circuit provides an average exposure value by calculating the exposure values. If the exposure sample is within a first exposure range, the refreshing logic circuit maintains the exposure parameter and accordingly drives the image sensor to capture a next image. If the average exposure value is within a second exposure range, the refreshing logic circuit adjusts the exposure parameter with a first exposure extreme and accordingly drives the image sensor to capture a next image. If the average exposure value is within a third exposure range, the refreshing logic circuit adjusts the exposure parameter with a second exposure extreme and accordingly drives the image sensor to capture a next image.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an optical mouse having an image capture chip,and more particularly to an image capture chip capable of effectivelyadjusting an exposure value.

2. Description of Related Art

Recently, image capture chips are widely used in various digital devicessuch as digital cameras, video cameras, and optical pointing devices.Image capture chips play an important role in capturing a projectedimage of an object for subsequent related digital image processing.Based on a theory of exposure, the image capture chip adjusts anexposure parameter according to an illumination of the object, therebydetermining a suitable exposure duration.

Thus, by using the adjusted exposure parameter, the correspondingaverage exposure value thereof is able to be converged within anormal-exposure range, even if the illumination of the object is toodark or too bright.

FIG. 1A is a diagram of a conventional image capture chip. Each of thepixel units PIX11˜PIXnm is a pixel circuit of the image sensor 100. Theimage capture chip 10, initially, reads captured image data line by lineand stores the pixel signals of the pixel units PIX11˜PIXnm via a signalreading circuit 130. The pixel signals of the signal reading circuit 130are amplified by an amplifier 150. Finally, the A/D converter 170converters the amplified pixel signals into a plurality of digitalpixels. Thus, a digital signal processor (DSP) 11 accordingly performsrelated image processing such as calculating the average exposure valueor displaying the captured image.

FIG. 1B is a diagram of the image sensor 100 of FIG. 1A. If a CMOS M2 isturned on according to a reset signal RES, the potential across anoptical diode PD is charged to a voltage Vrst. The voltage Vrstdecreases as the optical diode PD is exposed under the illumination ofthe image. Each row of sensor units PIX1 m˜PIXnm as shown in FIG. 1Acomprises its storage 131. When a NMOS M3 is turned on by a selectsignal RSEL2, the residual voltage across the optical diode PD istransformed into a current across an NMOS M1. The current charges acorresponding storage 131 of a signal reading circuit 130. The charge ofeach storage 131 is referred to as an illumination value of thecorresponding pixel unit.

The illumination intensity and the illumination duration of the opticaldiode PD are referred to as an exposure intensity and an exposureduration of the image sensor 100, respectively. Based on the theory“Exposure value=Exposure intensity*Exposure duration”, the exposurevalue can be adjusted if the exposure duration or the illuminationduration is changed. Hence, to maintain the exposure quantity, theexposure duration is decreased when the exposure intensity is increased.Alternatively, the exposure duration is increased when the exposureintensity is decreased.

Generally, an exposure parameter is provided for adjusting the exposureduration. For example, to increase the exposure value according to theconventional exposure control method, the exposure parameter is linearlyadded with a predetermined exposure parameter. Alternatively, fordecrease the exposure value, the exposure parameter is linearlysubtracted by a predetermined exposure parameter.

It is difficult, however, to define the predetermined exposure parameterof the conventional exposure control method. For example, if theexposure parameter is adjusted with an excessively large predeterminedexposure parameter, the illumination of a digital image is substantiallychanged. Thus, it is difficult to converge the corresponding exposurevalue into a normal-exposure range. Similarly, if the exposure parameteris adjusted by an excessively small predetermined exposure parameter,the illumination of the object is changed slightly. Thus, numerousadjustment steps are only required, resulting in slow convergence.Hence, the digital image is excessive dark or excessive bright due to along exposure duration, thus the image quality is adversely affected.

SUMMARY OF THE INVENTION

The object of the invention is to efficiently adjust an exposureparameter according to the illumination of a captured object. Thus, thecorresponding exposure value can be rapidly adjusted to be within thenormal-exposure range.

Accordingly, the present invention provides an image capture chip,comprising an image sensor, a calculating logic circuit, and arefreshing logic circuit. According to an exposure parameter, the imagesensor comprising a plurality of sensor units captures an image toprovide a plurality of exposure values. The calculating logic circuitcalculates an average exposure value according to the exposure values.

If the average exposure value is within a first exposure range, therefreshing logic circuit maintains the exposure parameter, andaccordingly drives the image sensor to capture a next image. If theaverage exposure value is within a second exposure range, the refreshinglogic circuit adjusts the exposure parameter according to a firstexposure extreme, and accordingly drives the image sensor to capture anext image. If the average exposure value is within a third exposurerange, the refreshing logic circuit adjusts the exposure parameteraccording to a second exposure extreme, and accordingly drives the imagesensor to capture a next image.

The first exposure range, is referred to as a normal-exposure range, thesecond exposure range is referred to as an over-exposure range, and thethird exposure range is referred to as an under-exposure range.

Furthermore, the image capture chip is capable of determining whetherthe captured image meets an image quality condition according to animage feature prior to determining whether the average exposure value iswithin the normal-exposure range.

Accordingly, the present invention provides an image capture chip,comprising an image sensor, a calculating logic circuit, and arefreshing logic circuit. According to an exposure parameter, the imagesensor comprising a plurality of sensor units captures an image toprovide a plurality of exposure values. The calculating logic circuitcalculates an average exposure value according to the exposure values.The refreshing logic circuit at least comprises a determining logiccircuit, which is capable of determining whether the captured imagemeets an image quality condition.

Thus, when the captured image meets the image quality condition, therefreshing logic circuit maintains the exposure parameter even if theaverage exposure value is within the over-exposure range or theunder-exposure range.

Additionally, both of the image capture chips can be disposed in anoptical mouse, for improving operational sensitivity of the opticalmouse.

Accordingly, the present invention provides an optical mouse with animage capture chip. The optical mouse comprises a light source, anoptical lens, an image sensor comprising a plurality of sensor units, acalculating logic circuit, and a refreshing logic circuit. The lightsource illuminates an object to obtain a reflected image. The opticallens projects the reflected image to result a projected image. The imagesensor captures the projected image according to an exposure parameterto provide a plurality of exposure values. The calculating logic circuitcalculates an average exposure value according to the exposure values.The refreshing logic circuit is capable of determining whether thecaptured image meets an image quality condition.

To determine whether the exposure parameter requires to be adjustment.The refreshing logic circuit is capable of distinguishing the imagequality of the captured image before or after determining whether thecorresponding average exposure value is within the normal-exposurerange.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become apparent by referring to the subsequentdetailed description of a preferred embodiment with reference to theaccompanying drawings, wherein:

FIG. 1A is a diagram of a conventional image capture chip;

FIG. 1B is a diagram of the image sensor 100 of FIG. 1A;

FIG. 2 is a diagram of an image capture chip of the present invention;

FIG. 3 is a flowchart of the exposure control method of the presentinvention;

FIG. 4 is a schematic diagram of the exposure parameter adjustmentprocess of the present invention;

FIG. 5 is a chronological chart of an image sensor reading an image ofthe present invention;

FIG. 6 is a schematic diagram of the exposed duration and the unexposedduration; and

FIG. 7 is a schematic diagram of an optical mouse of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The object of the invention is to efficiently adjust an exposureparameter according to the illumination of a captured object. Thus, thecorresponding exposure value can be rapidly adjusted to be within thenormal-exposure range.

FIG. 2 is a diagram of an image capture chip of the present invention.Image capture chip 400 comprises an image sensor 410 having a pluralityof sensor units 411, a calculating logic circuit 420, and a refreshinglogic circuit 430. When the image capture chip 400 captures an image,according to an exposure parameter, the image sensor 410 provides aplurality of exposure values via the sensor units 411. When receivingthe exposure values, the calculating logic circuit 420 calculates anaverage exposure value according to the exposure values. The refreshinglogic circuit 430 adjusts the exposure parameter according to theexposure sample to change the exposure duration of the image sensor 410.Thus, an unexpected average exposure value can be adjusted to be withinthe normal-exposure range.

FIG. 3 is a flowchart of the exposure control method of the presentinvention. Initially, Step S102 sets an exposure parameter of an imagesensor. Step S104 follows and sets the exposure duration of the imagesensor according to the exposure parameter, and then executes anexposure to capture an image via the image sensor. After exposure viathe image sensor, the voltage across the optical diodes PD in FIG. 1Aand FIG. 1B is read by the signal reading circuit 130, and the chargecorresponding to the voltage is stored in the corresponding storage 131.

Step S106 follows and provides the average exposure value according tothe charge of each storage 131. Step S108 follows and determines whetherthe average exposure value is in a normal-exposure range. If the resultof step S108 is positive, step 104 follows and maintains the presentexposure parameter and executes an exposure to capture a next image viathe image sensor.

If the result of step S108 is negative, step S110 follows and determineswhether the average exposure value is in an over-exposure range or anunder-exposure range. If the result of step S110 is positive, step S112follows and adjusts the exposure parameter according to an exposureextreme within the variable range of the exposure parameter. Step S104follows and executes an exposure to capture a next image according tothe adjusted exposure parameter via the image sensor.

For example, if the average exposure value is within the over-exposurerange, the image capture chip 400 calculates a new exposure parameter byaveraging a minimum exposure parameter and the present exposureparameter. Similarly, if the average exposure value is within theunder-exposure range, the image capture chip 400 calculates a newexposure parameter by averaging a maximum exposure parameter and thepresent exposure parameter.

If the result of step S110 is negative, step S114 follows and determineswhether the average exposure value is between the normal-exposure rangeand the over-exposure range, the third exposure range. If the averageexposure value is within the third exposure range, step S116 follows andcalculates a new exposure parameter by subtracting a predeterminedparameter from the present exposure parameter, and then, step S104follows and executes an exposure to capture a next image according tothe new exposure parameter via the image sensor.

If the result of step S114 is negative, step S118 follows and determineswhether the average exposure value is between the normal-exposure rangeand the under-exposure range, the fourth exposure range. If the averageexposure value is within the fourth exposure range, step S120 followsand calculates a new exposure parameter by adding a predeterminedparameter to the present exposure parameter, and then, step S104 followsand executes an exposure according to the new exposure parameter via theimage sensor.

If the average exposure value is not within the normal-exposure range,when the exposure parameter equals maximum exposure parameter, the imagesensor is not able to execute an exposure according to the illuminationof the captured image. Thus, step S122 follows and adjusts theillumination of the captured image by other auxiliary tools or methods.For example, a photoflash is used to illuminate the object, therebyenhancing the illumination of the captured image.

FIG. 4 is a schematic diagram of the exposure parameter adjustmentprocess of the present invention. The right scale Range_E can be dividedinto a plurality of sub-ranges defined by two exposure parameters, andsimilarly, the left scale Range_AE can be divided into a plurality ofsub-ranges defined by two average exposure values. The scale Range_AEincludes an over-exposure range 11, a high exposure range 20, anormal-exposure range 30, a low exposure range 40, and an under-exposurerange 51.

If the maximum value Max and minimum value Min of the exposure parameterare 235 and 20, respectively, a predetermined exposure parameter M is10, a present exposure parameter is 230, and an average exposure valuecaused by the present exposure parameter is within the over-exposurerange 11. Additionally, an average exposure value is within thenormal-exposure range 30 if its corresponding exposure parameter isbetween 90˜120. Thus, the exposure control method is used for adjustingthe present exposure parameter until the present exposure parameter iswithin the 90˜120 range.

According to the present invention, initially, the new exposureparameter is calculated by averaging the minimum value Min and thepresent exposure parameter. Thus, the new exposure parameter is equal to125 calculated by averaging 20 and 230. The image capture chip thenexecutes an exposure to capture a next image according to the newexposure parameter. Thus, a new average exposure value caused by the newexposure parameter is provided and can be within the high exposure range20. According to the exposure control method of the present invention,the new exposure parameter must be subtracted from the predeterminedexposure parameter M, 10. Hence, a new exposure parameter is equal to115 or between 90˜120. Obviously, a new average exposure value caused bythe new exposure parameter can be converged within the normal-exposurerange 30. Following the steps as mentioned, to achieve a new averageexposure value within the normal-exposure range 30, the present exposureparameter is adjusted only twice according to the present invention.

Contrary to the present invention, by using the conventional exposurecontrol method, the exposure parameter is adjusted by continuouslyadding or subtracting a predetermined exposure parameter L until thecorresponding average exposure value is within the normal-exposure range30. If the predetermined exposure parameter L is 20, a new exposureparameter equal to 110 is derived by calculating the equation: 230−6*20.Thus, a new average exposure value resulting from the new exposureparameter is converged into the normal-exposure range 30. According tothe above description, the present exposure parameter must be adjustedsix times. Hence, the conventional exposure control method requires moreadjustment steps than the present invention. Obviously, the exposurecontrol method of the present invention has faster convergence speedthan the conventional method.

FIG. 5 is a chronological chart of an image sensor of the presentinvention reading an image. In FIG. 5, T_(p) is pixel time which refersto a pixel reading duration, N_(ppl) is the total number of pixel timesfor reading a line, thus, a line time T_(Nppl) is defined as“T_(Nppl)=T_(p)*N_(ppl)”. N_(lpf) is the total number of line times forreading a frame, thus, a frame time T_(Nlpf) is defined as“T_(Nlpf)=T_(p)*N_(ppl)*N_(lpf)”. Additionally, V_(sync) is asynchronous signal for receiving pixel signals by the image sensor, andR_(sel) _(—) _(n) is a select signal for selecting which one of the rowof the pixel units is to be charged.

For example, suppose that the pixel time T_(p) is 1 μs, number N_(ppl)is 40, and the number N_(lpf) is 20, thus a line time T_(Nppl) is 40 μsaccording to the product of the pixel time T_(p) and the number N_(ppl).The frame time T_(Nlpf) or the longest exposure duration is equal to 800μs according to the product of the line time T_(Nppl) and the numberN_(lpf). Hence, a frame rate is equal to 1250 frame/sec by calculatingthe inverse value of the frame time T_(Nlpf).

Accordingly, if fixing the pixel time as T_(p) and the number asN_(ppl), the longest exposure duration T_(NlPf) and the frame rate canbe adjusted by only adjusting the number N_(lpf). For example, if thenumber N_(lpf) is increased to 40, the longest exposure durationT_(Nlpf) is increased to 1600 (μs), thus the frame rate is decreased to625 (frame/sec), increasing the exposure duration.

With reference to the illumination as shown in FIG. 1B, when capturingan image, the image sensor can enable the NMOS M2 by the reset signalRES to determine a start time of the optical diode PD to be illuminated,thereby controlling the exposure values of the image sensor 100.

Thus, the present invention also provides two parameters, whichcomprising a pixel number N_(p) and a line number N_(l), to set astarting time of the reset signal RES. The start time of the resetsignal RES is adjusted by the pixel number N_(p) and the line numberN_(l), thus the unexposed duration T_(unexp) is able to be calculated bythe pixel number N_(p) and line number N_(l) as the following equation:T_(unexp) = T_(p) * (N_(p) + N_(ppl) * N_(l))   = T_(p) * N_(p) + T_(Nppl) * N_(l)

For example, suppose that the pixel time T_(p) is 1 μs, the numberN_(ppl) is 40, and the number N_(lpf) is 20, thus, the frame timeT_(Nlpf) or the longest exposure duration is equal to 800 μs.Additionally, suppose that an unexposed duration T_(unexp) is equal tothe duration of reading three lines and ten pixels. Thus, the pixelnumber N_(p) is 10, and the line number N_(l) is 3. Hence, following theequations as mentioned, the unexposed duration T_(unexp) is equal to 130μs.

Additionally, an exposed duration T_(exp) is calculated by subtractingthe unexposed duration T_(unexp) from the longest exposure duration asshown in following equation:T _(exp) =T _(Nlpf) −T _(unexp)

Hence, the exposed duration T_(exp) is equal to 670 (μs). If theillumination of the image is increased, the exposure duration can bedecreased by adjusting the pixel number N_(p) and line number N_(l) toobtain a suitable exposure parameter. For example, the pixel numberN_(p) is increased to 30 and the line number N_(l) is maintained, andthe unexposed duration T_(unexp) is then increased to 150 ps and theexposed duration T_(exp) is decreased to 650 μs.

FIG. 6 is a schematic diagram of the exposed duration and the unexposedduration. RES_1 to RES_n are represented as n-rows reset control signal,respectively. The V_(line) _(—) ₁ to V_(line) _(—) _(n) are representedby n-rows pixel exposure duration, respectively.

Generally, to maintain stable frame rate, adjustment of the numberN_(lpf) is not required. Hence, if the frame time T_(Nlpf) ismaintained, the reset signal RES can be determined by adjusting theunexposed duration T_(unexp) or the exposure duration of the imagesensor.

Furthermore, the present invention provides an optical mouse comprisingthe image capture chip. If the feature of an image is recognized by theimage capture chip, the optical mouse is capable of processing relatedimage procedures without adjustment the exposure parameter. Hence, todetermine whether the exposure parameter requires adjustment, the imagecapture chip is capable of distinguishing the image quality of thecaptured image before or after determining whether the correspondingaverage exposure value is within the normal-exposure range.

To achieve the above, the refreshing logic circuit 430 as shown in FIG.2 also comprises a determining logic circuit 431, which is capable ofdetermining whether the captured image meets an image quality condition.

The image quality condition is determined according to features of aone-dimensional image. For example, a sinusoidal function wave isobtained according to the brightness of each pixel, number of featuresof the one-dimensional image can then be obtained by counting the numberof peaks in the sinusoidal function wave. Thus, according to the numberof features, the image capture chip 400 is capable of determiningwhether the captured image meets the image quality condition. Similarly,in a two-dimensional image, the image quality condition is determined bya two-dimension image processing method. For example, a two-dimensionalfunction wave is drawn according to the brightness of each pixel. It canthen determine the number of features according to a plurality ofcharacteristics such as rolling hills of the two-dimensional functionalwave. Thus, the image quality of the two-dimensional image is determinedby comparing the number of features with a predetermined table, whichstores various conditions with feature number and corresponding imagequality.

The method for determining image quality is not limited to the methoddisclosed, but can include any image processing method.

If the captured image meets the image quality condition, the exposureparameter is maintained even if the average exposure value is within theover-exposure range or the under-exposure range. In addition, if thecaptured image does not meet the image quality condition, and theaverage exposure value is within the over-exposure range or theunder-exposure range, the exposure parameter is adjusted.

FIG. 7 is a schematic diagram of an optical mouse of the presentinvention. Optical mouse 500 comprises a light source 510, an opticallens 520, and a image capture chip 530, wherein the light source 510 islight emitting diode (LED).

When the LED illuminates an object, light is reflected to the opticallens 520 and projected on the image capture chip 530, whereby the imagecapture chip 530 executes subsequent related image process procedures.

While the invention has been described by way of example and in terms ofthe preferred embodiments, it is to be understood that the invention isnot limited to the disclosed embodiments. To the contrary, it isintended to cover various modifications and similar arrangements (aswould be apparent to those skilled in the art). Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

1. An image capture chip, comprising: an image sensor with a pluralityof sensor units, capturing an image to provide a plurality of exposurevalues when determining an exposure parameter; a calculating logiccircuit, calculating an average exposure value of the exposure values;and a refreshing logic circuit, maintaining the exposure parameter ifthe average exposure value is within a first exposure range, andaccordingly driving the image sensor to capture a next image; adjustingthe exposure parameter according to a first exposure extreme if theaverage exposure value is within a second exposure range, andaccordingly driving the image sensor to capture a next image; andadjusting the exposure parameter according to a second exposure extremeif the average exposure value is within a third exposure range, andaccordingly driving the image sensor to capture a next image; wherein,the first exposure range is between the second exposure range and thethird exposure range, and, the first exposure extreme and the secondexposure extreme are referred to as a maximum parameter and a minimumparameter, respectively, within the variable range of the exposureparameter.
 2. The image capture chip of claim 1, the refreshing logiccircuit further comprising a determining logic circuit, determiningwhether the captured image meets an image quality condition; wherein,the refreshing logic circuit maintains the exposure parameter if thecaptured image meets the image quality condition and accordingly drivesthe image sensor to capture a next image.
 3. The image capture chip ofclaim 1, wherein the refreshing logic circuit further adjusts theexposure parameter according to a predetermined parameter if thecaptured image is within a fourth exposure range, and accordinglydriving the image sensor to capture a next image; wherein, the fourthexposure range is between the first exposure range and the secondexposure range.
 4. The image capture chip of claim 1, wherein therefreshing logic circuit further adjusts the exposure parameteraccording to a predetermined parameter if the captured image is within afifth exposure range, and accordingly driving the image sensor tocapture a next image; wherein, the fifth exposure range is between thefirst exposure range and the third exposure range.
 5. The image capturechip of claim 1, wherein the exposure parameter comprises a pixelnumber, a line number, and a total number of line times for reading aframe.
 6. An image capture chip, comprising: an image sensor with aplurality of sensor units, capturing an image to provide a plurality ofexposure values when determining an exposure parameter; a calculatinglogic circuit, calculating an average exposure value of the exposurevalues; and a refreshing logic circuit at least comprising a determininglogic circuit, determining whether the captured image meets an imagequality condition; wherein, if the captured image meets the qualitycondition, the refreshing logic circuit maintains the exposure parameterand accordingly drives the image sensor to capture a next image, and ifthe captured image does not meet the quality condition, the refreshinglogic circuit determines the exposure parameter and accordingly drivesthe image sensor to capture a next image.
 7. The image capture chip ofclaim 6, wherein, if the captured image meets the image qualitycondition, and the average exposure value is within a first exposurerange, a second exposure range, or a third exposure range, therefreshing logic circuit maintains the exposure parameter, andaccordingly drives the image sensor to capture a next image; if thecaptured image does not meet the image quality condition, and, if theaverage exposure value is within the second exposure range, therefreshing logic circuit adjusts the exposure parameter according to afirst exposure extreme, and accordingly drives the image sensor tocapture a next image; if the average exposure value is within the thirdexposure range, the refreshing logic circuit adjusts the exposureparameter according to a second exposure extreme, and accordingly drivesthe image sensor to capture a next image; wherein, the first exposurerange is between the second exposure range and the third exposure range,and, the first exposure extreme and the second exposure extreme arereferred to as a maximum parameter and a minimum parameter,respectively, within the variable range of the exposure parameter. 8.The image capture chip of claim 7, wherein, if the captured image iswithin a fourth exposure range, the refreshing logic circuit furtheradjusts the exposure parameter according to a predetermined parameterand accordingly drives the image sensor to capture a next image;wherein, the fourth exposure range is between the first exposure rangeand the second exposure range.
 9. The image capture chip of claim 7,wherein if the captured image is within a fifth exposure range, therefreshing logic circuit further adjusts the exposure parameteraccording to a predetermined parameter and accordingly drives the imagesensor to capture a next image; wherein, the fifth exposure range isbetween the first exposure range and the third exposure range.
 10. Theimage capture chip of claim 6, the exposure parameter comprises a pixelnumber, a line number, and a total number of line times for reading aframe.
 11. An optical mouse, comprising: a light source, illuminating anobject to generate a reflected image; an optical lens, projecting thereflected image to generate a projected image; an image sensor with aplurality of sensor units, capturing the projected image to provide aplurality of exposure values when determining an exposure parameter; acalculating logic circuit, calculating an average exposure value of theexposure values; and a refreshing logic circuit, maintaining theexposure parameter if the average exposure value is within a firstexposure range, and accordingly driving the image sensor to capture anext image; adjusting the exposure parameter according to a firstexposure extreme if the average exposure value is within a secondexposure range, and accordingly driving the image sensor to capture anext image; and adjusting the exposure parameter according to a secondexposure extreme if the average exposure value is within a thirdexposure range, and accordingly driving the image sensor to capture anext image; wherein, the first exposure range is between the secondexposure range and the third exposure range, and, the first exposureextreme and the second exposure extreme are referred to as a maximumparameter and a minimum parameter, respectively, within the variablerange of the exposure parameter.
 12. The optical mouse of claim 11, therefreshing logic circuit further comprising a determining logic circuit,capable of determining whether the projected image meets an imagequality condition; wherein, if the projected image meets the imagequality condition, the refreshing logic circuit maintains the exposureparameter and accordingly captures a next image via the image sensor.13. The optical mouse of claim 11, wherein the refreshing logic circuitfurther adjusts the exposure parameter according to a predeterminedparameter if the average exposure value is within a fourth exposurerange, and accordingly drives the image sensor to capture a next image;wherein the fourth exposure range is between the first exposure rangeand the second exposure range.
 14. The optical mouse of claim 11,wherein the refreshing logic circuit further adjusts the exposureparameter according to a predetermined parameter if the average exposurevalue is within a fifth exposure range, and accordingly drives the imagesensor to capture a next image; wherein a fifth exposure range isbetween the first exposure range and the third exposure range.
 15. Theoptical mouse of claim 11, the exposure parameter comprises a pixelnumber, a line number, and a total number of line times for reading aframe.
 16. An exposure control method, for adjusting an exposureparameter of an image sensor, comprising following steps: setting theexposure parameter of the image sensor; exposing with the exposureparameter to result a plurality of exposure values; resulting an averageexposure value by calculating the exposure values; determining whetherthe average exposure value is within a first exposure area, a secondexposure area, or an third exposure area; maintaining the exposureparameter if the average exposure value is within a first exposurerange; adjusting the exposure parameter according to a first exposureextreme if the average exposure value is within a second exposure range;and adjusting the exposure parameter according to a second exposureextreme if the average exposure value is within a third exposure range;wherein, the first exposure range is between the second exposure rangeand the third exposure range, and, the first exposure extreme and thesecond exposure extreme are referred to as a maximum parameter and aminimum parameter, respectively, within the variable range of theexposure parameter.
 17. The exposure control method of claim 16,wherein, the exposure control method further comprises following step ofadjusting the exposure parameter according to a predetermined parameterif the average exposure value is within a fourth exposure range;wherein, the fourth exposure range is between the first exposure rangeand the second exposure range.
 18. The exposure control method of claim16, wherein, the exposure control method further comprises followingstep of adjusting the exposure parameter according to a predeterminedparameter if the average exposure value is within a fifth exposurerange; wherein a fifth exposure range is between the first exposurerange and the third exposure range.
 19. The exposure control method ofclaim 16, wherein, the exposure parameter comprises a pixel number, aline number, and a total number of line times for reading a frame.